Character addressing system

ABSTRACT

In a cathode-ray tube display, digital signals representative of characters to be generated are divided into two groups representing the two directions of deflection. A first group provides a linear region in which uniform deflection steps are generated for each signal increment, while a second group provides a nonlinear region in which varied deflection increments are generated for each signal increment. The nonuniform regions provide higher resolution in those areas where curves normally occur and less resolution in the remaining areas thus providing higher character resolution in specified positions on the same size matrix. The nonuniform deflection is obtained from associated decoders through a weighted addressing system which provides nonuniform current increments independent of the digital data input.

United States Patent Jones 1 Feb. 8, 1972 [54] CHARACTER ADDRESSINGSYSTEM 3,165,729 1/1965 Richman 340/324 A 3,335,416 8/1967 Hughes..340/324 A [721 Invent Richard Red 3,403,286 9/1968 Carlock et al..340/324 A x [73] Assignee: International Business MachinesCorporation, Armonk, NY. Primary ExaminerDavid L. Trafton Fl d J 30 1969An0meyl-lanifin and Jancin and Joseph J. Connerton 1e 21 Appl. 110.;837,790 1 ABSTRACT In a cathode-ray tube display, digital signalsrepresentative of [52] us. or. ..340/324 A, 315/18 characters begenerated e divided into two groups [51] "Goa 3/14 representing the twodirections of deflection. A first group 5 Field of Search 340/324 24 A.315/1 2 provides a linear region in which uniform deflection steps are178763 3 generated for each signal increment, while a second groupprovides a nonlinear region in which varied deflection incre- [56]Reerem Cited ments are generated for each signal increment. Thenonuniform regions provide higher resolution in those areas where UNITEDSTATES PATENTS curves nonnally occur and less resolution in theremaining areas thus providing higher character resolution in specified3,1 19,949 1/ 1964 Greatbatch et a]. ..3 1 5/26 positions on the samesize matrix The nonuniform deflection 3,422,304 1/1969 is obtained fromassociated decoders through a weighted ad- 3479453 11/1969 dressingsystem which provides nonuniform current increments independent of thedigital data input. 315211241 7/1970 6 Claims, 7 Drawing FiguresINTENSITY 1s CONTROL ,55 57 DEFL DEFL omv new LINEAR 1 NON-LINEARDECODER DECODER 7 4/ x POSITION Y POSITION 55 REG REG 25 51 x INPUT 27 YlNPUT REG XFER PATENTEIJFEB 8 I972 3.641.556

SHEET 1 0? V FIGJ-V INTENSITY CONTROL 5? DEFL DEF L DRIV DRIV NON-LINEARoecoosn DECODER 43 45j s3 mm 4 mm x POSITION Y POSITION 55 REG REG I I II I 5 I /56 Y3 Y2 Y1 25 W XINPUTI 27H REG XFER 29- s TIMING BI J31 21CONTROL II INVENTOR AM I 6617a. m RICHARD A. JONES PAIENTEUFEB 8 I872 3.641 .556

sum 2 OF 2 FIG.20

F1630 FIG. 3b I IG-3c- CHARACTER ADDRESSING SYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates to a displaydevice'and more particularly to an improved charactergeneratordeflection system suitable for use with cathode-ray tubes fordisplaying the generated characters.

2. Description of the Prior Art In known cathode-ray tube charactergeneration systems, characters are normally generated on a linearcoordinate matrix on the CRT screen either as a sequence of strokes ordots in which the size-of the matrix determines the resolution. Anexample of a stroke character. generator using a uniform rectangularmatrix is shown in US. Pat. No. 3,334,304,

Asynchronous Character Generator for Successive Endpoint Definition,issued to R. J. Fournier et al., Aug. 1, 1967. However, where the sizeof the coordinate matrix is limited, uniform resolution in all areas ofthe character tends to produce an undesirable font, particularly inthose areas where curves tend to occu'nAn analysis of stroke charactersindicates that most endpoints occur at the extremities and center of thecharacter such that increased resolution in this area will improvecharacter quality. While improved resolution can normally be provided byincreasing the size of the character matrix, this is undesirable becauseof added circuit complexity, flicker problems and storage capacitylimitations. Where the video information is stored in arecirculatingbuffer, for example, an increase of the character matrix from 7X7 to 10l0 effectively more than doubles the storage requirements of thedisplay. The present invention is directed to a means for increasingcharacter resolution in a cathode-ray tube display without any addedcomplexity in size or cost.

SUMMARY OF THE INVENTION In one arrangement according to the invention,digital signals indicative of characters to be generated on a CRTdisplay are decoded into analog signals suitable for'deflecting the beamof the cathode-ray tube. Rather than generate the characters on'auniform coordinate grid, the present invention utilizes a lineardeflection for onecoordinate of the character (the horizontal), and anonlinear deflection for the second coordinate of the character. Thisnonlinear deflection is obtained by weighting the individual decodeddeflection signals such that smaller deflection units aflording higherresolution are provided at those areas where the curved segments of mostcharacters tend to occur. Those areas of the matrix not normallyassociated with curved characters utilize higher deflection unitsresulting in greater spacing without character degradation.

Accordingly, a primary object of the present invention is to provide animproved character generator circuit.

Another object of the present invention is to provide an improveddeflection system for improving the resolution of specific characterareas by modifying the deflection control to provide a nonuniformdeflection in one of the character coordinates.

Another object of the present invention is to provide an improvedcharacter generator'having a linear and nonlinear addressable gridsystem designed to improve the aesthetic appearance of characters.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 illustrates in block logical form a preferred embodiment of thepresent invention.

FIG. 2a illustrates in schematic form a binary weighted decoder shown inblock form in FIG. 1.

FIG. 2!; illustrates in schematic form a nonlinear weighted decodershown in block form in FIG. 1.

FIG. 3 illustrates character display formats.

FIG. 3a illustrates a character generated by using the conventionaladdressable grid matrix.

FIGS. 3b and 3c illustrate characters generated in accordance with theaddressable matrix of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings andmore particularly to FIG. 1 thereof, binary coded signals are appliedfrom a data source which might comprise, for example, a data processorsuch as Central Processing Unit 11 through input lines 21 and 23 to theX input register 25 and the Y input register 27, respectively. A databyte comprising six binary bits is used for each character stroke, threebits for the horizontal deflection and three hits for the verticaldeflection. The preferred embodiment of the present invention utilizesan 8X8 character matrix which can be provided by three bits for eachcoordinate, each three-bit signal designating the end point of thevector. In response to a transfer signal on the line 29 from timing andcontrol circuit 31, the contents of the X and Y input register aretransferred through conductor pairs labeled X1, X2, X3 and Y1, Y2 andY3, with X1 and Y1 representing the lowest order binary bits, to the'Xand Y Position Registers 33 and 35, respectively. The preferredembodiment of the instant invention is described as operating indouble-ended, push-pull configuration such that each binary designationutilizes separate lines to represent the l and 0 states. The X and Yposition registers 33 and 35 comprise count-up, countdown counters orregisters which are incremented or decremented in accordance with theinput signals applied from the associated input registers. A +X signalon line 34 will increment Position Register 33 by one, a -X signal online 36 will decrement the counter by one. While various count-up,countdown counters are known in the art, one preferred embodiment isshown in US. Pat. No. 3,403,286 (IBM Docket 16866009), Digital CathodeRay Deflection System" filed by F. R. Carlock et al., Dec. 27, 1966.Since the present invention is directed only to character generation,the initial positioning for each character has been omitted asunnecessaryto an understanding of the present invention. However, eithera separate deflection coil could be utilized to initially position thebeam for character generation, oralternatively, the Xand Y positionregisters 33 and 35 could be large .enough to accommodate both thecharacter position and individual stroke deflection signals.

In response to a transfer signal from timing and control circuit 31 online 37, the contents of the X and Y Position Re gisters 33 and 35 aretransferred through conductors 39 and 41 to their associated decoders 43and 45, respectively. The horizontal decoder 43, as more fully describedhereinafter, is a conventional binary weighted linear decoder in whichuniform increments or decrements of current are provided for eachpositive of negative signal applied to the X position register 33. Thevertical decoder 45 in the preferred embodiment of the instant inventionis a nonlinear decoder in which the digital addresses, when decoded,generate nonuniform incremental steps to provide higher resolution inthe upper, lower and center areas and lesser resolution in thenoncritical intermediate area as more fully described hereinafter. Inresponse to a control signal on line 46, the cumulative X signals onlines 47 and 49 from horizontal linear decoder 43 are transferred vialines 47 and 49 to their respective buffer transistors 51 and 53,respectively. Buffer transistors 51 and 53 function to isolate thedecoder output from the associated deflection drive circuits 55 and 57,respectively. The output from the deflection drivers 55 and 57 are thenapplied to the horizontal yoke winding 59 of CRT 61. Likewise, theoutput from the vertical decoder 45 on lines 60 and 62 is appliedthrough associated buffer transistors 63 and 65 and associateddeflection drivers 67 and 69 to the vertical yoke winding 71 of CRT 61.

As the individual horizontal and vertical deflection signals are appliedto the associated yoke windings 59 and 71 in the manner above described,the grid 73 is maintained unblanked by means of intensity controlcircuit 75. Intensity control circuits for maintaining a CRT beam in theunblarrked condition during character generation are well known in theart such that a block showing is considered to constitute adequatedescription. However, one conventional method is to include an extra bitin the end point data for intensity control information.

Referring now to FIG. 2a, there is illustrated in block schematic formdetails of the horizontal linear decoder shown as block 43 in FIG. 1.The decoder as shown is a double-ended decoder operating on three bitsranging from the lowest order bit XI through X2 and X3. Since thedecoder operates in a push-pull fashion, a latch register comprisinglatch circuits 81, 83 and 85 is employed, each stage having binary l andoutputs, the respective outputs of which in turn are connected to binaryweighted resistors 87, 89 and 91 and 87, 89' and 91'. Latch circuits arewell-known components in a data processor, are similar to flip-flops ortriggers except for timing considerations related to reversal of state.For a detailed description of latch registers and latch circuits,reference is made to U.S. Pat. No. 3,115,574 to G. T. Paul et al.,entitled High Speed Multiplier," FIGS. 33-35 and related description.The values of 4R, 2R and R are merely relative to reflect the binaryweighting of each binary bit in proportion to its place value. Actualvalues would vary according to the deflection system employed, thecharacter size, etc., and such values represent mere designconsiderations known to those skilled in the art. The outputs on lines47 and 49, representing the cumulative horizontal deflection signals,are connected to the buffer transistors 51 and 53 as shown in FIG. 1. Asshown in the grid arrangements of FIG. 3, the horizontal decodersprovide uniform horizontal deflection increments for each input signalpermutation. Since the characters or character segments may be generatedeither from left to right or right to left, depending on the specificcharacter configuration, the decoder 43 responds to the output from theX position register 33 (Fig. l) which may be incremented or decrementedin single steps heretofore described.

Referring now to FIG. 2b, the nonlinear vertical decoder 45 utilized inthe preferred embodiment of the invention is shown in block schematicfonn. The three-bit coded signals for each character segment are appliedto the appropriate latch register stages 93, 95 or 97, the individualoutputs of which are connected to resistors 101, 103 and 105 and 101,103 and 105'. However, instead of being binary weighted as in thehorizontal deflection, the vertical decoder stages are weighted in aratio of 1:315 to reflect the expansion factor of l which has been addedto the weighting values corresponding to the binary place values of 2and 4. The weighting value corresponding to the place value of 1 has notbeen expanded. For purposes of comparison, the low order bit of decoder45 is also designated as 4R, the next more significant bit as 4/3 R, andthe most significant bit 4/5 R. The relative ratio of the currents forthe eight possible input combinations to the decoder is shown indecreasing binary increments in the table below, the tabulated codedvalues corresponding to those shown in Figures 3b and 30.

It should be noted that the values for current indicated in the tableabove are relative, the actual values again being determined by variousdesign considerations associated with the specific cathode-ray tubedisplay. The outputs from nonlinear decoder 45 are applied throughassociated conductors 60 and 62 to the vertical winding 71 of themagnetic yoke.

Referring now to FIG. 3, there is illustrated a sequence of charactersincluding one generated by the conventional rectangular grid and severalcharacters generated in accordance with the preferred embodiment of thepresent invention, all characters being generated on an 8X8 matrix.Referring inifially to FIG. 3a, the character 5 is shown on an 8X8coordinate matrix, eight segments representing the maximum resolutionwhich can be achieved from a three-bit by three-bit word. The numeral 5has been selected as exemplary of problems associated with theconventional coordinate grid matrix. As shown thereon, and particularlyat the normally curved center and lower portions of the figure, thelimited resolution provides a very poor image quality such that thenumeral 5" cannot be readily distinguished from the letter Further,purely from a human factors standpoint, the appearance of the characteris undesirable. One way and the conventional way of improving imagequality is to increase the resolution of the available grid from 8X8 tosome higher number depending on the degree of resolution desired.However, this requires a larger word size, and the entire systemincluding the input registers, the position registers, decoders, bufferand even the data processor transmitting the data bytes would allnecessarily be larger to accommodate the larger word such that thissolution from an economic standpoint is impractical.

A practical solution for improving character quality is provided by theinstant invention. The drawings of FIG. 3 are not intended to indicate aprecise character size, but are enlarged and exaggerated to identify theproblem. However, the relative proportions correspond to charactersgenerated by the instant invention. Referring to FIGS. 3b and 30, thereare shown several characters generated on a variation of an 8X8 matrixutilizing the principles of the instant invention. It will be noted thatthe upper lines of the matrix (111, the lower lines (000,001) each haveareas of fine resolution and that a series of fine resolution lines areshown in the center portion (010, 011, 100, 101). However, both theintermediate lower (001 to 010) and intermediate upper (101 to 110)sections provide a relatively gross resolution in this area. However, itis apparent from FIGS. 3b and 3c that gross resolution in this area doesnot constitute a problem but from an aesthetic standpoint, actuallyenhances the character appearance. Thus it is seen that although thedigital data input is not increased, improved overall resolution isachieved by using grossly resolved data in noncritical areas and finelyresolved data in critical areas. The corresponding vertical addresses ofeach unit of deflection are shown in FIGS. 3b and 3c and the imagequality, as readily apparent, is substantially enhanced over thatprovided by the conventional square address matrix of FIG. 3a.

While the advantages of improved character quality may not be readilyapparent from the exaggerated drawings of FIG. 3, they are apparent in adisplay system when it is recognized that in actual size where up to 960characters may be displayed on a cathode-ray tube screen ofapproximately 14 inches. The invention affords improved image qualitywith no required change in input data and minimum change from theconventional square grid matrix.

While the invention has been shown and described with reference to aspecific embodiment, it is apparent that other modifications to eitheror both deflection systems to alter character appearance are encompassedwithin the teaching of the subject invention, and that while theinvention has been particularly shown and described with reference to apreferred embodiment thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention.

What is claimed is:

1. In a cathode-ray tube character generator, the combinationcomprising:

a cathode-ray tube having beam deflection means and intensity controlmeans;

a source of video data representative of characters to be displayed;

said video data being applied for each stroke of said character, firstand second decoder means for converting said video data into deflectionsignals;

said first decoder means being adapted to produce uniformly weightedlinear signals;

said second decoder producing a nonuniformly weighted incrementalsignals, and

means connectingsaid uniformly weighted and said nonuniformly weightedsignals to said beam deflection means to produce linear deflectionsignals in one direction and nonlinear deflection in the orthogonaldirection whereby the resolution of the generated characters issubstantially improved.

2. Apparatus of the type claimed in claim 1 wherein the output of saidfirst decoder means has a plurality of regions within its output range,said regions including areas of high resolution and low resolution.

3. Apparatus of the type claimed in claim 2 wherein said areas of highresolution include the upper, lower and medial regions of saidcharacters.

4. A method for decoding digital signals each having a plurality ofgroups representing coordinates of display stroke end points of acharacter to be displayed with increased resolution, comprising thesteps of: p

l. weighting a first binary data bit of a first digital signal group bya first value corresponding to the binary place value of said firstbinary data bit to provide a first analog signal;

2. weighting a next more significant binary bit of said first digitalsignal group by a second value corresponding to the binary place valueof said next more significant binary data bit plus an expansion factorto provide a second analog signal;

3. weighting a second more significant binary data bit of said firstdigital signal group by a third value corresponding to the binary placevalue of said second more significant binary data bit plus saidexpansion factor to provide a third analog signal;

4. summing said first, second and third analog signals to provide afirst coordinate of a display stroke end point.

5. The method of claim 4 further comprising the steps of:

5. weighting each binary data bit of a second digital signal group byvalues corresponding to the binary place values of each of said binarydata bits of said second digital signal group to provide analog signals;

6. summing said analog signals to provide a second coordinate of saiddisplay stroke end point.

6. The method of claim 5 further comprising the steps of:

7. repeating Steps '1 through 6 for each digital signal representing adisplay stroke end point of a character to be displayed whereby saidcharacter has a high resolution concentrated in upper, medial, and lowerregions, and has a lower resolution between said upper and said medialand between said medial and said lower regions.

1. In a cathode-ray tube character generator, the combinationcomprising: a cathode-ray tube having beam deflection means andintensity control means; a source of video data representative ofcharacters to be displayed; said video data being applied for eachstroke of said character, first and second decoder means for convertingsaid video data into deflection signals; said first decoder means beingadapted to produce uniformly weighted linear signals; said seconddecoder producing a nonuniformly weighted incremental signals; and meansconnecting said uniformly weighted and said nonuniformly weightedsignals to said beam deflection means to produce linear deflectionsignals in one direction and nonlinear deflection in the orthogonaldirection whereby the resolution of the generated characters issubstantially improved.
 2. Apparatus of the type claimed in claim 1wherein the output of said first decoder means has a plurality ofregions within its output range, said regions including areas of highresolution and low resolution.
 2. weighting a next more significantbinary bit of said first digital signal group by a second valuecorresponding to the binary place value of said next more significantbinary data bit plus an expansion factor tO provide a second analogsignal;
 3. weighting a second more significant binary data bit of saidfirst digital signal group by a third value corresponding to the binaryplace value of said second more significant binary data bit plus saidexpansion factor to provide a third analog signal;
 3. Apparatus of thetype claimed in claim 2 wherein said areas of high resolution includethe upper, lower and medial regions of said characters.
 4. summing saidfirst, second and third analog signals to provide a first coordinate ofa display stroke end point.
 4. A method for decoding digital signalseach having a plurality of groups representing coordinates of displaystroke end points of a character to be displayed with increasedresolution, comprising the steps of:
 5. The method of claim 4 furthercomprising the steps of:
 5. weighting each binary data bit of a seconddigital signal group by values corresponding to the binary place valuesof each of said binary data bits of said second digital signal group toprovide analog signals;
 6. summing said analog signals to provide asecond coordinate of said display stroke end point.
 6. The method ofclaim 5 further comprising the steps of:
 7. repeating Steps 1 through 6for each digital signal representing a display stroke end point of acharacter to be displayed whereby said character has a high resolutionconcentrated in upper, medial, and lower regions, and has a lowerresolution between said upper and said medial and between said medialand said lower regions.